Conventional optical packages assume that the scene radiance does not vary while it is being analyzed. If the scene radiance does in fact vary—for example, because the line-of-sight (LOS) of the instrument changes for an inhomogeneous scene—then the radiance may not be analyzed accurately. If the LOS change is random, this can become a significant source of analysis error. When sounding planetary atmospheres, scene inhomogeneity due to the presence of clouds is a significant source of noise or uncertainty. Conventional sounding or retrieval algorithms attempt to remove inhomogeneity using methods called “cloud clearing,” “hole hunting,” and various cloud-mask methods. None of these methods, however, can unambiguously determine the degree of scene inhomogeneity for an individual field-of-view (FOV) because they require the observation of multiple or adjacent fields of view. Determining the degree of scene inhomogeneity for each observed instrument FOV independent of cloud-clearing or other method may significantly improve the accuracy of the sounding algorithms used to retrieve atmospheric parameters of interest. Knowing that the FOV contains a homogeneous scene also permits neglecting the effect of small, uncontrollable, and random LOS changes on the radiance and sounding analysis.